These tips will help increase your chances of getting a sourdough ear.
A sourdough ear is the prominent flap of crust that rises in the oven where the dough was scored.
To get an ear, first of all, you must have a healthy sourdough starter that's vigorous and consistently doubles in size.
The dough must ferment long enough to build gases and strength. My bulk fermentation guide goes in depth on this topic!
Build surface tension when shaping to increase oven spring and to help the dough maintain its shape. A taut dough will more likely have an ear.
Use a sharp blade or bread lame to cut a shallow angle slash into the dough. Cut at a 45º angle and ¼-½" deep.
Use a Dutch oven to trap steam. You can also add a couple of ice cubes or mist the loaf to increase steam. Steam will make for better oven spring.